Vehicle brake



T. K. MACE VEHICLE BRAKE Feb. 16, 1954 2 Sheets-Sheet 1 Filed June 24, 1950 Emma KEMP MACE by M W Ann- 61M2 Feb. 16, 1954 T. K. MACE I VEHICLE BRAKE 2 Sheets-Sheet 2 Filed June 24, 1950 Tia/was KEMP MAC Patented Feb. 16, 1954 OFFICE 2,669,328 VEHICLE BRAKE Thomas Kemp Mace, Birmingham, England Application June 24, 1950, Serial No. 170,079

Claims priority, application Great Britain June 28, 1949 7 Claims.

1 This invention relates to improvements in vehicle brakes of the type in which pivoted or sliding shoes each comprising a web and a flange carrying a friction lining are mounted within a rotatable drum, and in the off position of the brake the resultant of the forces acting on a shoe is such as to urge it towards the drum but means are provided for maintaining a small predetermined clearance between the shoe or at least the major portion of it and the drum. Thus friction between the shoes and the, drum in the ofi position of the brake is reduced to a minimum and there is no risk of the leading shoe being picked up by the drum.

The object of my invention is to provide a brake of the kind specified above having improved means for maintaining a small predetermined clearance between the surface of a shoe lining and the brake drum in the ofi position of the brake and for maintaining that clearance substantially constant as the lining wears.

According to my invention, in a brake of the kind specified, a curved yicldable lever or arm substantially concentric with but of less radius than a shoe is pivoted at one end on afixed pivot on the back-plate of the brake adjacent to the end of the shoe which is engaged by an actuator, and the other end of the lever has a finger extending through a cut-away portion of the flange of the shoe adjacent to the shoe anchorage and projecting radiallyfor a predetermined distance beyond the contour of the sur face of the shoe lining, an intermediate point on the lever engaging an abutment on the shoe web about the middle of the length of the shoe. When the brake is in the off or released position the extremity of the finger on the lever is in'contact with the brake drum and the radial position of the abutment on the shoeis such that the lever holds the shoe out of engagement with the drum and maintains a small predetermined clearance between the surface of the shoe lining and the drum. Thus the only drag on the drum is that due to the contact of the finger with the drum and in practice that drag is so small as to be negligible. In a brake having leading and trailing'shoes a lever as described above need only be provided for the leading shoe, but in a brake having two leading shoes a lever will be provided for each shoe. g When the brake is applied the shoe is moved outwardly into engagement with the drum and the finger on the lever is forced inwardly to conform to the contour of the shoe lining. The

lever, or at least the part of it between the extremity of the finger and the abutment on the shoe, is made with suificient resilience to allow the finger to yield inwardly when the brake is applied, the lever recovering to withdraw the shoe from engagement with the drum when the brake is released again.

If the abutment on the shoe engages the lever about the middle of its length, the lever is acting on the shoe through a leverage of two to one and the component of the weight of the shoe tending to swing it outwardly into engagement with the drum may be partially balanced by a spring so that the thrust to be exerted by the drum on the finger of the lever need only be very small.

Two practical brakes embodying my invention are illustrated by way of example in the accompanying drawings in which:

Figure 1 is a front elevation of a complete brake.

Figure 2 is a section on the line 2-2 of Figure 1.

Figure 3 is a section on the line 3-3 of Figure 1.

Figure 4 is a front elevation of one half of a brake embodying a modified form of lever.

Figure 5 is a section of the brake shown in Figure 4.

The brake illustrated in Figures 1 to 3 is a two-leading-shoe brake having two single-ended hydraulic cylinders H], II rigidly mounted on a stationary back-plate 12. One brake shoe 13 has a pivotal engagement with an abutment on the cylinder II, the end I 3 of the shoe being formed with a part-circular recess bearing against a part-cylindrical surface on the abutment [3 so that the shoe can move angularly about the abutment. The other end [3''' of the shoe is received in a recess in the piston ['0' of the cylinder l0 and engages the inner end 01' the recess. The other brake shoe l4 hasa similar pivotal engagement at one end with an abutment on the cylinder [0 and the other end of the shoe is received in a recess in the piston H" of the cylinder H.

The rest of the mechanism is the same for each shoe and only one need be described. Taking the shoe l4, an arcuate lever I5 is pivoted on the back-plate about a fixed pivot pin l6 adjacent to the end of the shoe which is engaged by the piston of the cylinder II. The lever is a sheetsteel pressing and is substantially concentricwithv but of smaller radius than the shoe. The end gof, the lever remote from the pivot is cranked over to form a finger I'l curved to the same radius as the surface of the shoe. A small pad of friction material l8 of substantially the same thickness as the lining is of the shoe is secured to the outer surface of the finger. The flange of the shoe adjacent to its anchored end is cut away on one side as shown at 20 for the passage of the lever and the cut-away portion is bridged by a strip 2! which is welded to the flange and retains the lever against lateral movement relative to the shoe as well as reinforcing the flange.

At an intermediate point in its length the inner edge of the lever engages an abutment formed by the cranked and radiused end 22 of a plate or strip 23 welded or otherwise secured to the web of the shoe and extending radially inwards from the inner edge of the web.

The lever or at least the part of it between the intermediate abutment and the finger I! has a certain degree of resilience so that the finger can yield inwardly under the reaction of the drum on the pad i3 when the brake is applied. A portion of the weight of the shoe tending to swing it outwardly about its lower end is counterbalanced by a light spring 24 connected between the shoe web and a fixed anchorage 25 on the back-plate.

The resultant of all the forces acting on the shoe in the off position of the brake is such that the shoe is lightly biassed towards the drum. The lower brake cylinder l l is connected through a union 26 to a pipe line leading to a master cylinder (not shown) and the two brake cylinders are connected by a pipe 21 so that equal forces are applied to the pistons of both cylinders when the master cylinder is actuated.

In the off position of the brake the pad IS on the lever I is in contact with the brake drum 28 and the radial position of the abutment 22 is such that the lever maintains a small predetermined clearance between the lining IQ of the shoe and the surface of the drum.

When the brake is applied the shoe is moved outwardly into engagement with the drum and at the same time the finger on the end of the lever is forced inwardly, the lever having sufficient resilience to allow for this. When the brake is released the lever recovers and urges the pad l8 outwardly beyond the contour of the shoelining and maintains it in contact with the drum while the lever acting on the shoe through the abutment 22 withdraws the shoe from contact with the drum and maintains the predetermined small clearance between the surface of the shoe lining and the drum.

The pad it will wear at a rate substantially equal to or less than that at which the shoe lining wears so that as the shoe lining wears down the clearance between the lining and the drum which is determined by the position of the abutment 22 relative to the lever will not vary appreciably.

The brake illustrated in Figures 4 and 5 is of the type in which the shoe is not positively located at its anchored end but has a sliding and rocking engagement with an abutment so that the shoe can automatically take up a centralized position relative to the drum.

The shoe 3% in this case has a radiused end face 45! adapted to rock and slide on an inclined abutment M on the closed end of the cylinder 42 which actuates the other shoe. The rounded other end 43 of the brake shoe engages in a recess $4 of the actuator piston 45. Thus the shoe in Figure 4 has a rocking engagement at its lower end with the'piston of the actuator and its upper slightly rounded end 40 has a sliding engagement with the abutment 4|. When the brake is applied the shoe moves outwardly and upwardly and its upper end slides radially outward through a small distance on the abutment M.

The lever 30 which corresponds to the lever H: in the brake shown in Figures 1 to 3 is modifled in that the finger which projects through the flange of the shoe and carries the pad l8 for engagement with the brake-drum is a member 3| separate from the main part of the lever to which it is pivotally connected by a stud 32.

The two parts 30 and 3| are frictionally clamped together by a spring washer 33 under a nut 34 on the stud to provide substantial frictional resistance against relative angular movement.

The main part 30 of the lever has on its inner edge about the middle of its length a surface 35 adapted to engage an abutment on the shoe 36 formed by a cranked and radiused lug 31 on a plate 38 welded to the web of the shoe and providing an anchorage for one end of a spring 39, the other end of which is secured to the back plate near the actuator 42 at 16. It will be noticed from the drawing that the pull of the spring 39 is substantially at right angles to the surface ii, and this spring is suflicient to maintain the shoe in position in View of the fact that the finger 3i is in contact with the drum in the off position of the brake. Dropping of the shoe downward'is prevented partly by the spring and partly by the engagement of the shoe end 43 with the recess 44, in the actuator piston.

The lever 39 or the part of it between the lug 31 and the stud 32 has a certain amount of resilience so thatit can yield under pressure, or if the lever is rigid the lug 31 is made resilient so that it can yield under pressure.

Initially when the brake is assembled the member 3i is set so that the pad l8 projects appreciably beyond the contour of the shoe lining. When the brake is first applied the shoe end 40 slides on the abutment M to centralize the shoe relative to the drum and the pad iii and shoe lining are urged against the surface of the drum. The reaction of the drum on the pad l3 causes the lever to yield to its permitted extent and causes the member 3i to move angularly about the stud 32 until the surface of the pad lies in the same contour as the surface of the shoe lining which is then in engagement with the drum.

When the brake is released the lever recovers and urgesthe pad l8 outwardly beyond the contour of the shoe lining to maintain the small predetermined clearance between the lining and the drum.

1 claim:

1. A brake of the kind specified comprising an arcuate shoe mounted within a rotatable drum including a web, an arcuate flange and a friction lining carried by said flange, a stationary back-plate, an anchorage on the back-plate for one end of the shoe, an actuator on the backplate engaging the other end of the shoe, a yieldable lever pivotally mounted at one end on the back-plate adjacent to the end of the shoe engaged by the actuator, a finger on the other end of the lever projecting through the flange of the shoe into engagementwith the drum adjacent to the anchored end of the shoe, andan abutment on the shoe web for engagement by the lever at an intermediate point in the length of the said lever.

2. A brake of the kind specified comprising an arcuate shoe mounted within a rotatable drum including a web, an arcuate flange and a friction lining carried by said flange, a stationary back-plate an anchorage on the back-plate for one end of the'shoe, an actuator on the backplate engaging the other end of the shoe, an arcuate yieldable lever substantially concentric with and of less radius than the shoe mounted to pivot at one end about a fixed point on the back-plate adjacent to the end of the shoe which is engaged by tthe actuator, a finger on the other end of the lever extending through a cut-away portion of the flange of the shoe adjacent to the shoe anchorage and projecting radially for a predetermined distance beyond the contour of the surface of the shoe lining for engagement with the drum, and an abutment on the shoe web about the middle of the length of the shoe for engagement by the lever.

3. A brake as in claim 2 in which said finger carries a pad of friction material for engagement with the brake drum.

4. A brake as in claim 2 in which said abutment on the shoe Web for engagement by the lever comprises a cranked lug secured to and projecting radially inwards from said web.

5. A brake as in claim 2 in which said finger is a separate member pivoted to the lever, said pivot incorporating frictiona1 resistance against relative angular movement between the lever and the finger.

6. A brake as in claim 2 in which the cut-away portion of the shoe flange is bridged by a strip which is welded to the flange and retains the lever against lateral movement relative to the shoe.

7 A brake as in claim 2 wherein said shoe is mounted to rock about its lower end and including a, spring which partially balances the weight of the shoe tending to rock it outwardly about said end into engagement with the drum.

THOMAS KEMP MACE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,311,765 Loweke Feb. 23, 1943 2,350,868 Benn June 6, 1944 2,371,554 Scott-Iverson Mar. 13, 1945 FOREIGN PATENTS Number Country Date 44,436 France Oct. 22, 1934 (Addition to No. 756,347) 579,108 Great Britain July 23, 1946 

